Radiation-sensitive compositions are routinely used in the preparation of imageable materials including lithographic printing plate precursors. Such compositions generally include a radiation-sensitive component, an initiator system, and a binder, each of which has been the focus of research to provide various improvements in physical properties, imaging performance, and image characteristics.
Recent developments in the field of printing plate precursors concern the use of radiation-sensitive compositions that can be imaged by means of lasers or laser diodes, and more particularly, that can be imaged and/or developed on-press. Laser exposure does not require conventional silver halide graphic arts films as intermediate information carriers (or “masks”) since the lasers can be controlled directly by computers. High-performance lasers or laser-diodes that are used in commercially-available image-setters generally emit radiation having a wavelength of at least 700 nm, and thus the radiation-sensitive compositions are required to be sensitive in the near-infrared or infrared region of the electromagnetic spectrum. However, other useful radiation-sensitive compositions are designed for imaging with ultraviolet or visible radiation.
There are two possible ways of using radiation-sensitive compositions for the preparation of printing plates. For negative-working printing plates, exposed regions in the radiation-sensitive compositions are hardened and unexposed regions are washed off during development. For positive-working printing plates, the exposed regions are dissolved in a developer and the unexposed regions become an image.
Various negative-working radiation compositions and imageable elements containing polymer binders are known in the art. Some of these compositions and elements are described for example in U.S. Pat. No. 6,569,603 (Furukawa), U.S. Pat. No. 6,309,792 (Hauck et al.), U.S. Pat. No. 6,582,882 (Pappas et al.), U.S. Pat. No. 6,787,281 (Tao et al.), U.S. Pat. No. 6,899,994 (Huang et al.), U.S. Pat. No. 7,175,969 (Ray et al.), U.S. Pat. No. 7,172,850 (Munnelly et al.), U.S. Pat. No. 7,332,253 (Tao et al.), U.S. Pat. No. 7,326,521 (Tao et al.), U.S. Patent Application Publications 2003/0118939 (West et al.), 2005/0003285 (Hayashi et al.), and 2007/0184380 (Tao et al.), and EP 1,079,276A1 (Lifka et al.), and EP 1,449,650A1 (Goto).
Partially hydrolyzed poly(vinyl acetate) has also been used as a binder in imageable elements as described for example in EP 1,788,448A1 (Williamson), but these elements require the presence of a water-soluble poly(vinyl alcohol) overcoat (outermost layer). In addition, U.S. Pat. No. 7,338,741 (Aoshima et al.) describes the use of poly(vinyl acetate) with a degree of hydrolysis of at least 80 mol %.